Doctor blade



April 20, 1965 E. WARNER 3,179,083

DOCTOR BLADE Filed Sept. 19, 1960 Unite This invention is concerned with the application of coating substances to moving webs or sheets. More particularly the invention deals with a doctor device for smoothing and leveling the coating substance after an excess of the substance has been applied to the web to assure a substantially uniform application of the coating substance to the web. The doctor device may have utility in a variety of processes but is of particular utility where the coating substance may have quick setting characteristics.

A case in point, though the device is not limited to such use, is in the manufacture of coated paper wherein in accordance with the teachings of US. Patent No. 2,229,- 621 an excess of coating is applied to a web of paper, the coating being comprised of dispersed pigment and adhesive in an aqueous medium, filter cake forms on and adjacent to the web surface and excess fluid coating above the filter cake formation is removed by the doctor. The

present invention can be said to represent an improvement over US. Patent 2,729,192 and co-pending application for Letters Patent S.N. 52,438 filed August 29, 1960 (now US. Patent 3,084,663), both to Edgar Warner, in that a rotating doctor rod for the application of quick set materials examples of which are adhesives, resin coatings or mineral pigment coatings as used in the paper industry which have ben treated with a waterproofing agent to render them less absorbent.

While doctor devices of the rotating rod type have been used to apply such quick setting substances, some difficulty has been experienced because of the tendency for minor amounts of these fluid substances to work behind the rotating rod into the rod holder and, at times, to accumulate to the extent the doctor rod is forced from the holder. The present invention represents a relatively simple yet extremely valuable solution to that problem.

According to the invention a rotatable rod is mounted in a holder throughout its working length, the holder comprising a longitudinal socket having parallel terminal edges spaced apart a distance less than the diameter of the rod to expose a substantial portion of its circumference face to define a working surface, a portion of the socket embracing the rod being spaced from the rod to define therewith a longitudinal cavity or chamber, which may be flooded with a fluid through suitable ports to wash the rod surface as it is rotated in the socket. Additionally, means may be provided to clean out the cavity.

The fluid may be varied according to the character of the coating being applied and may be water or any one of a variety of solvents.

The invention will now be more fully described, reference being made to the attached drawing, wherein,

FIG. 1 is a front elevation of one form of the structure embodying the invention,

FIG. 2 is a sectional view taken along the line 2-2 of FIG. 1,

FIG. 3 is a rear elevation somewhat reduced in size of the structure shown in FIGS. 1 and 2, certain parts removed for clarity, but illustrating with FIG. 2, a cleaning device for the chamber,

FIGS. 4 and 5 are cross-sectional views illustrating further structures embodying the invention,

FIGS. 6, 7 and 8 are schematic views of at least some of the coater arrangements in which the invention has utility; and finally,

FIG. 9 represents the embodiment of FIGURE 4 as seen from the top of FIGURE 4.

States atent Considering now FIGS. 1, 2 and 3, it will be seen that the doctor rod 10 is mounted in a holder 20 throughout its working width. The rod It) is of small diameter, approximately to /2 inch; usually fashioned from tool steel and provided with a chrome plated wear resistant surface by the usual plating methods.

As illustrated, in part in FIG. 1, the rod is of such length that terminal ends extend beyond the ends of the holder 20. To these terminal ends is affixed at driving means in this case sprocket 2, engaged by chain 4, which is driven by a sprocket 6. Sprocket 6 is mounted on a driven shaft 8 powered by a motor-speed reduction gear combination M. If desired, both ends of the rod may be driven by extending shaft 8 at the opposite end of the holder and merely duplicating the sprockets and chains to drive this end of the doctor rod. This arrangement is particularly advantageous where the doctor blade is of considerable length, as, for example, on a paper machine, to minimize torsional stress introduced into the rod. The drive means shown is exemplary and the invention of course is not to be interpreted as limited to the particular details illustrated.

The rod holder 20 in which the doctor rod 10 is mounted and as seen in FIGS. 1 and 2, in particular, is comprised of two plate-like elements, preferably of a corrosion resistant material 22, 24 fastened together, by rivets, spot welds, or the like, 26 spaced along the length of the holder. Between them these elements define a channel-like socket 28 which surrounds the rod 10 for greater than half of its circumference. The terminal edges 32, 34 of elements 22 and 24 are thus disposed in parallel, spaced relation a distance less than half the diameter of the rod to retain it seated in the channel 28. The exposed circumferential surface of the rod 10 thus defines a work ing surface which, when placed against the surface of a web or sheet of material which is moved relative to it,

. will act to doctor fluid substances previously applied to the surface to form a level coating while removing the excess of the fluid coating substance over and above that amount of less fluid coating substance required to assure a uniform coverage of the substrate web or sheet being coated.

As is shown in the sectional view of FIG. 2 the holder element 24 is shaped generally in the form of a question mark so that it defines with element 22 a channel-like cavity or chamber of greater cross-sectional volume than that required merely to receive the doctor rod 10. Thus with the rod 10 emplaced within the channel 28, a sizable void of unoccupied volume is created which is in the form of a cavity or chamber 36 of uniform cross-section defined in part by the rod 10, and in the case of the structure of FIGS. 1 and 2 the two sides of the generally question mark shaped holder element 24. In this particular embodiment it will also be noted that a second chamber or cavity 33 is also defined by the holder elements 22 and 24 and the surface portion of rod 10. In some cases the second chamber is neither necessary nor desirable in which case the alternative structure of FIG. 5 may provide a satisfactory coating doctor, though it must be emphasized that in all cases at least one cavity or chamber is embraced within the holder 20 behind the rod 10. The chamber or cavity 36 thus formed between holder 20 and rod 10 may thus be flooded or filled, or supplied from a continuous source, with a solvent which will remove from the rods surface any adhesive material which might collect on the rod and by reason of its properties be carried between the rod surface and the terminal edges 32 or 34 of the holder elements 22 and 24 and could build up on the rod 10 to the point where it might mar the surface of the coating which it permits to remain on the web, or

the entire surface width of the rod 10.

in extreme cases, be popped out or sprung from its seat in channel 28.

The rod It) is received, as illustrated, in the looped or bent upper end of the question mark-shaped element. Depending angularly from the looped upper end is a tail. A major portion of the rod is embraced by the socket part of the holder and a minor portion of the rod is a working surface disposed between the socket terminal edges.

The solvent substance, be it water, alcohol, a resin solvent or whatever, depending on the character of the adhesive may be admitted to chamber 36 by means of a nipple 39 seated in a suitable port in communication with the interiorly disposed chamber 36. In many cases it may be found desirable to provide the entire chamber with a series of such ports and nipples 3% wherein the admitted solvent substancewill be uniformly distributed throughout chamber-36 to act with equal efiectiveness on In other cases it may be satisfactory to admit the solvent through one opening wherein the solvent material is caused to flow into the elongated chamber 36 and out of the chamber through the open ends thereof where the holder terminates.

Generally, it is not'necessary to close the ends of the chamber 36, these open ends acting as exits for the solvent substance which is caused to flow in the chamber. The over-flow may be caught in suitable drain troughs 43 and piped to a point removed from the coating operation. In other cases, where the flow of solvent is relatively slow, the chamber 36 may drain directly back into the coating itself since the total accumulation of solvent in the coating may be so insignificant as not to affect the characteristics of the adhesive or other properties of the coating composition.

As seen in FIGS. 1 and 2, the holder elements 22, 24 are riveted or spot welded together at 26 to form a unitary holder structure 2%) which must be mounted in some manner on the coater structure, be it a simple blade coater as illustrated in FIG. 6, a blade and roll coater as illustrated in FIG. 7, or a pool-type of coater as illustrated in FIG. 8.

In FIGS. 1 and 2, the doctor blade assembly would be of the so-called rigid blade type in that holder elements 22 and 24 are clamped between two bar members 42 and 44 in such a manner that the holder is inflexible, that is there can be little if any flexure of the holder 20 in a longitudinal direction. This mounting is illustrated in detail in Warner Patent 2,598,733.

Referring now to FIGS. 2 and 3, it will be seen that a means of cleaning chamber 36 is disclosed. While as a general rule, the fit of the rod 16 within the channel 28 is so close that there is little if any leakage from the working face of the rod into the chamber 36 nonetheless, it may be found advantageous to clean out the chamber 36 from time-to-time, or under extreme conditions on a continuous basis. Such a condition might arise 'where the substance being doctored is particularly quick setting or may be applied under extremely high viscosity or tackiness, such that even minute amounts, if permitted to accumulate or form a deposit on the surface of rod 14} would rapidly build up to mar the coating which it allows to remain on the web and eventually to cause displacement of the rod 1th from holder 26. As illustrated in FIG. 3, this cleaning device may be comprised of a flexible cord or similar material which is caused to pass longitudinally through chamber 36. Obviously the diameter of this cleaning cord is suffieient to touch walls of the chamber 36 though its bulk should not be of such characteristics as to completely fill the chamber. An example of such an item would be a conventional round brush having a central cord of small diameter yet the bristles embrace a volume much greater than that of the cord, though this embraced volume could permit the passage of a fluid between the bristles.

As schematically illustrated this cleaning cord 47, if flexible enough could easily be played out from an upwind reel 51 through the chamber 36 in rod holder 20 to a wind-up reel 53. Obviously, these reels could be hand operated. However, it is in most cases more convenient to have them mechanically driven in which case reels 5]. and 53 would be driven via motor M, and sprockets 56, 56 57 and 57 and chains 58, 53 such that the cleaning cord would be caused to transverse through the chamber 36.

Either intermittent or continuous operation of motor M would provide intermittent or continuous cleaning as might be desirable under a given set of circumstances.

Further, it is believed also obvious that the cleaning cord could be either reuseable or of the disposable type as may also prove desirable.

As is also clear from FIG. 2, the structure therein shown includes a second chamber 38 defined between holder elements 22 and 24 along with the rod Ml. All that has been stated above may be applied to this chamber also. This particular embodiment of the invention, thus afiords particular utility where it might be desirable to clean the surface of rod 16 with one solvent in chamber 36 and thereafter wash or neutralize the solvent by a further cleansing of the rod 19 in which case chamber 38 would be provided with ports and could also be provided with a cleaning means.

Referring now to FIGS. 4 and 5, it will be seen that these figures illustrate further embodiments of the invention. FIG. 4 shows rod 30 mounted in a holder 50, the latter being comprised of two complementary sheet metal elements 52, 54 and a central strip support member 89. The two elements 53, 54 define a channel having an enclosed volume greater than that of the rod 30 in cross-sectional area such that there is again formed a longitudinal cavity 56 which is divided into two equal parts by the support member The rod 19, in the FIGS. 2, 4 and FIG. 5 embodiments, is supported and maintained in contact with the terminal edges of the holder elements by engagement with portions 24A and 66A or support member 8% of the socket, i.e. by engagement with elements 24 and 66. The socket portions 24A and 66A and member 89 respectively are areas removed from the terminal edges of the socket and engage the rod away from, roughly opposite, the rod working surface. The socket portions 24A, 66A, 89 are disposed between the terminal edges of the sockets of the respective holders.

In the illustration of this form of the invention, the rod 30 is provided with equally spaced circumferential grooves 31 such that the surface of the rod has a threadlike profile configuration. The extr me terminal ends 58 and 59 of the holder are crimped inwardly toward the rod 30 and have serrated inner edges which ride in the circumferential grooves 31. The end of support strip 56 is also serrated to ride in extremely close contact with the grooved surface of rod 3t). This feature and the novel results obtained therefrom are clearly disclosed and claimed in the co-pending application, S. N. 52,438 of Edgar Warner, filed August 29, 1960 (now US. Patent 3,084,663).

Of course, the structure illustrated may be used in conjunction with a smooth surfaced rod also in which case the terminal edges 58 and 59 of the holder elements 53 and 54 are, in the previous case, spaced apart a distance less than half the diameter of the rod, but are not crimped inwardly to the degree shown in FIG. 4.

In the case where it is desired to utilize both halves of the divided longitudinal chamber or cavity 56, the holders may be provided with suitable parts and nipples 61 in the manner of that described above. If, however,

the chamber 56 is to contain one solvent, the support elements 53 and 54 may be riveted or spot welded together and mounted between rigid supporting bars 42, 44.

FIG. 5 illustrates a somewhat simplified structure from that disclosed in FIGS. 2 and 4, in that the holder 60 is comprised of two elements 66 and 67 so configured as to define but a single longitudinal chamber or cavity 69 behind the rod 10. As also illustrated the element 66 may comprise a flexible support 71 for the entire doctor structure. In most cases, however, it is preferable to form the holder as a unit which is subsequently mounted on a support since this latter arrangement avoids potential fabrication and replacement problems.

It will be appreciated that the grooved rod arrangement of FIG. 4 can also be incorporated into the structure of FIGS. 2 and 5, and that the chamber cleaning elements, described in connection with FIG. 3 can also be included with the structure of FIGS. 4 and 5.

Turning now to FIGS. 6, 7 and 8 it is to be noted that these figures are to be considered merely as illustrating the versatility of the doctor blade structures previously described and are not intended to limit its utility.

FIG. 6 illustrates the device as utilized with a resilientsurfaced back-up roll 80 wherein the blade structure would be flexibly mounted, as suggested in FIGS. 4 and 5. The coating is applied to web W by applicator roll 81 dipping into coating trough 82.

FIG. 7 illustrates the device as used in a blade coater wherein the holder may be of the type shown in either FIGS. 2, 4 and 5, that structure FIG. 5 being illustrated schematically. Again applicator roll 83 dips in the trough 84 to carry an excess of coating to the web W which is drawn or partially wrapped over the doctor rod 10 to remove excess coating.

FIG. 8 discloses the unique doctor structure as applied to a pool type coater where the web W is drawn down over a resilient surfaced roll 85 and the doctor blade form a nip into which a pool of coating material C is formed and through which the web W passes before passing into the nip. Again the structural features of either FIGS. 2, 4 or 5 may be used as desired.

In view of the description of the invention and its utility it will be obvious that changes may be made therein which fall Within the spirit and scope thereof. The invention is therefore to be limited only as defined in the appended claims, wherein what is claimed is:

1. A doctor blade structure for use in coating sheets and webs that comprises an elongated rod working member;

a holder means for revolvably supporting said rod throughout the working length of said rod, said holder including a first and second holder element, each consisting in a strip of predetermined crosssection,

said first holder element having a cross-sectional shape in the form of a question mark having a looped upper end that ends in a terminal edge in close contact with the rod circumference throughout the working length of the rod and an angular tail depending therefrom, said rod being at least partially received in said upper end,

said second holder element being fastened to said first holder element and having another terminal edge in close contact with the rod circumference spaced apart less than half the rod circumference from the first-said terminal edge, thereby to revolvably embrace said rod throughout the working length of the rod between the terminal edges of the first and sec ond elements,

said upper end of said first element at a position removed from the first-said edge defining part of the boundary of a cavity for the passage therethrough of a fluid for cleaning said rod;

said rod circumference forming an additional part of the cavity boundary; and

first and second port means in said holder, both communicating with said cavity and being spaced apart longitudinally along said holder, at least one of which port means is intermediate the ends of said holder, for introducing rod washing fluid into said cavity via one of said port means and withdrawing such fluid via the other of said port means.

2. A doctor blade structure according to claim 1 wherein said rod has a diameter in the range from about A; to about /2 of an inch.

3. A doctor blade structure for use in coating sheets and webs comprising an elongated rod working member;

a holder revolvably supporting said rod throughout the working length of the rod, said holder comprising a longitudinal channel-like socket embracing a major portion of said rod and having parallel terminal edges spaced apart a distance less than the rod diameter and in close contact throughout the working length of the rod with the circumferential face of the rod to expose between said edges a minor portion of said rod to define a rod working surface, a portion of said socket removed from said terminal edges being spaced from said rod to define therewith a longitudinal cavity, and a second portion of said socket holding said rod in contact with said terminal edges; and first and second port means in said holder, both communicating with said cavity and being spaced apart longitudinally along said holder, at least one of which port means is intermediate the ends of said holder, for introducing rod washing fluid into said cavity via one of said port means and withdrawing such fluid via the other of said port means.

4. A doctor blade structure according to claim 3 wherein said second portion of said socket is a means defining two spaced apart mutually coextensive longitudinal chambers.

5. A doctor blade structure according to claim 3 wherein at least one end of said rod extends beyond the end of said holder for connection to a means for rotating the rod.

6. A doctor device as defined in claim 3 wherein said holder is mounted on a flexible support providing for longitudinal flexure of the holder and said rod.

7. A doctor device as defined in claim 3 wherein said holder is mounted in a rigid support.

8. A doctor blade structure as defined in claim 3 wherein the rod working surface is circumferentially grooved.

9. A doctor blade structure as defined in claim 3 wherein said holder is comprised of a pair of complementarily shaped elements joined together to form said socket and wherein said second portion of said socket comprises a blade like support element interposed between said holder elements and in engagement with that portion of the surface circumferential of the rod emplaced within said socket.

10. A doctor blade structure as defined in claim 9 further including port means in said support element for establishing communications between said chamber portions.

11. A doctor blade structure according to claim 3 wherein said rod has a diameter in the range from about A; to about /2 of an inch.

12. A doctor blade structure for use in coating sheets and webs comprising an elongated rod working member;

a holder revolvably supporting said rod throughout the working length of the rod, said holder comprising a longitudinal channel-like socket embracing a major portion of said rod and having parallel terminal edges spaced apart a distance less than the rod diameter and in close contact throughout the working length of the rodwith the cirof the circumference of said rod and having parallel tercumferential face of the rod to expose between minal edges spaced apart a distance less than the diamsaid edges a minor portion of said rod to define eter of the rod to expose a portion of its circumferential a rod working surface, said socket having an surface as a working surface, at least a portion of the area removed from said terminal edges defining 5 socket embracing the rod and removed from said termia longitudinal support member means for ennal edgesbeing spacedtherefrom to define therewith a gaging said rod remote from said working surcavity, and a flexible brush-like member movable longiface and maintaining said rod in Cont ct with tudinally through said cavity, disposed within said cavity, said terminal edges, at least a portion of said and extending throughout said cavity.

socket removed from said terminal edges being 10 spaced from said rod to define-therewith a longi- References Cited by the'Examiner tudinal cavity;,and UNITED STATES PATENTS first and second port means in said holder, both ,2221 441 11/40 Charters communicating with said cavity and being spaced 2598733 6/52 Warner 113 118 apart longitudinally along said holder, at least 15 2729192 1/56 i one of which port means is intermediate the Zf731916 1/56 Koch i 52 X ends of said holder, for introducing rod washing 3031872 5 /62 Kusters X fluid into said cavity via one of said port means n and withdrawing. such fluid via the other of said FOREIGN PATENTS portlmeans. 20 572,062 9/45 Great Britain.

13. A doctor device comprising a rotatable rod sup- 532,849 11/56 Canada,

ported throughout its working length, a holder revolv- I ably supportingsaid length,the holder comprising a longi- RICHARD NEVIUS Pnmary Examme tudinal socket surrounding said rod for greater than half JOSEPH B. SPENCER, Examiner. 

1. A DOCTOR BLADE STRUCTURE FOR USE IN COATING SHEETS AND WEBS THAT COMPRISES AN ELONGATED ROD WORKING MEMBER; A HOLDER MEANS FOR REVOLVABLY SUPPORTING SAID ROD THROUGHOUT THE WORKING LENGTH OF SAID ROD, SAID HOLDER INCLUDING A FIRST AND SECOND HOLDER ELEMENT, EACH CONSISTING IN A STRIP OF PREDETERMINED CROSSSECTION, SAID FIRST HOLDER ELEMENT HAVING A CROSS-SECTIONAL SHAPE IN THE FORM OF A QUESTION MARK HAVING A LOOPED UPPER END THAT ENDS IN A TERMINAL EDGE IN CLOSE CONTACT WITH THE ROD CIRCUMFERENCE THROUGHOUT THE WORKING LENGTH OF THE ROD AND AN ANGULAR TAIL DEPENDING THEREFROM, SAID ROD BEING AT LEAST PARTIALLY RECEIVED IN SAID UPPER END, SAID SECOND HOLDER ELEMENT BEING FASTENED TO SAID FIRST HOLDER ELEMENT AND HAVING ANOTHER TERMINAL EDGE IN CLOSE CONTACT WITH THE ROD CIRCUMFERENCE SPACED APART LESS THAN HALF THE ROD CIRCUMFERENCE FROM THE FIRST-SAID TERMINAL EDGE, THEREBY TO REVOLVABLY EMBRACE SAID ROD THROUGHOUT THE WORKING LENGTH OF THE ROD BETWEEN THE TERMINAL EDGES OF THE FIRST AND SECOND ELEMENTS, SAID UPPER END OF SAID FIRST ELEMENT AT A POSITION REMOVED FROM THE FIRST-SAID EDGE DEFINING PART OF THE BOUNDARY A CAVITY FOR THE PASSAGE THERETHROUGH OF A FLUID FOR CLEANSING SAID ROD; SAID ROD CIRCUMFERENCE FORMING AN ADDITIONAL PART OF THE CAVITY BOUNDARY; AND FIRST AND SECOND PORT MEANS IN SAID HOLDER, BOTH COMMUNICATING WITH SAID CAVITY AND BEING SPACED APART LONGITUDINALLY ALONG SAID HOLDER, AT LEAST ONE OF WHICH PORT MEANS IS INTERMEDIATE THE ENDS OF SAID HOLDER, FOR INTRODUCING ROD WASHING FLUID INTO SAID CAVITY VIA ONE OF SAID MEANS AND WITHDRAWING SUCH FLUID VIA AND THE OTHER OF SAID PORT MEANS. 